Corrugated plastic relates to extruded double-walled plastic-sheets, or liners, produced from polypropylene or polyethylene resin. Corrugated plastic sheets have a generally similar construction to corrugated paperboard. There are two layers of sheets or skins connected by flutes disposed and connected therebetween to form the corrugated sheet. One type of corrugated plastic material is known as “plastic profile board.” As opposed to the flutes being undulating waves, as they are in paperboard corrugation and certain other plastic corrugated materials, the flutes in a plastic profile board are typically more like ribs and the profile is preferably extruded.
The plastic corrugated sheets can be transparent to allow light transmission, or they can be custom colored or translucent to signify an owner or manufacturer, or to block the transmission of light. The space between the outer skins act as an insulator. Graphics can also be applied to the outer surfaces and inner surfaces of the outer layers.
Chemically, corrugated plastic sheets are inert, with a neutral pH factor. At regular temperatures most oils, solvents and water have no effect, allowing the corriboard to perform under adverse weather conditions or as a product component exposed to harsh chemicals. Standard corrugated plastic sheets can be modified with additives, which are melt-blended into the sheet to meet specific needs of the end-user. Special products that require additives can include: ultra-violet protection, anti-static, flame retardant, custom colors, corrosive inhibitors, static-dissipative, among others.
The Wiley Encyclopedia in Packaging Technology (“Boxes, Corrugated” in The Wiley Encyclopedia of Packaging Technology, eds. Brody A and Marsh K, 2nd ed, John Wiley & Sons, New York) identifies the following standard flute designations used in the United States for paperboard corrugations:
FlutesFluteFlutesFluteFluteper linearthicknessper linearthicknessDesignationfoot(in)meter(mm)A flute33 +/− 3 3/16108 +/− 104.8B flute47 +/− 3⅛154 +/− 103.2C flute39 +/− 3 5/32128 +/− 104.0E flute90 +/− 4 1/16295 +/− 131.6F flute128 +/− 4  1/32420 +/− 130.8
Corrugated plastic can be used to form boxes and other similar containers. A variety of equipment has been used to convert paper and plastic corrugated material into boxes. The equipment is selected based on production run size, box size, and box quality in terms of tolerances and aesthetic appearance. This equipment includes flexographic, silk screen and digital printing machines; quick set, rotary, clam shell or flatbed die cut machines; and manual, ultrasonic welding, and automated folding and gluing machines for assembly.
Paper corrugated boxes are often used only once and then discarded. After a paper corrugated blank is converted into a box and used, it cannot typically be re-used in automated packaging lines designed to work with new, straight and flat boxes. This is in part because the major and minor flaps of a paper corrugated box will not return to their original vertical alignment after use, and in part because the creases and scores of a paper corrugated box lose integrity with each use. In such instances, the flaps become floppy or limp. Additionally, paper boxes cannot be washed or otherwise cleaned, and therefore cannot be reused in instances where sanitation is important (e.g., food items, etc.)
Therefore, the industry has long sought a re-usable container (i.e., one that can be cleaned or sanitized and then re-used), and has attempted to make a re-usable plastic corrugated container. As with paper corrugated containers, it is desirable that plastic corrugated containers are able to be used with conventional paper converting equipment (e.g., equipment that folds a cut/scored blank of material into a box). Previous methods to convert plastic corrugated material into boxes have used conventional paper corrugated converting equipment and process flow. This process flow includes making plastic corrugated material blanks to the appropriate size and then die cutting the blank using quick set, rotary, clam shell or flatbed die cutting machines. The die cut blanks are then assembled by bonding a glue tab and one of the panels to form a box. The blank may also be printed upon.
A lingering problem with current attempts to create a re-usable plastic corrugated container is that it must be able to return (after being used in a box form) to a flat state with the flaps aligned or coplanar with the side wall panels of the blank in order to be refolded in the box converting equipment. Industry efforts to this point have failed to provide such a container. In particular, the fold or score lines connecting the upper or lower flaps or panels to the side panels of the box must be able to bend (i.e., during a box forming process), and also have sufficient memory to revert to a straight position (i.e., coplanar or aligned with the box side panel) to again be reformed into a box (after sanitizing) using the converting equipment. However, the score lines cannot be made with too much memory so that after use, they have too much bounce-back or spring-back making them difficult for the converting equipment.
In addition, it is desirable to seal the edges to prevent intrusion of water, bacteria, or other debris, bugs or contaminants into the fluted area. This is particularly important for containers used with food and pharmaceutical products. Previous methods for sealing the edges of plastic corrugated material boxes have used either clam shell or flatbed die cutting machines during the converting process. The seal is formed in the die cut process using heat and pressure to pinch and weld together the inner and outer surfaces of the plastic corrugated material along the edge. This forms a sealed, but sharp edge, which is not acceptably ergonomically safe in most applications. Some limited success has been found using these processes for lighter densities of plastic corrugated material. While the process still leaves a sharp edge, the lighter densities make edge sealing acceptable for limited use applications, but not multiple re-use applications.
In addition to the above problems, it is also desirable to reduce the number of steps needed to create and process plastic corrugated boxes and to increase the processing speed. Due to environmental concerns, it is anticipated that many companies will insist on or otherwise turn to re-usable containers in the near future. Thus, the demand for such containers will rise and the speed of the plastic container processing will become a more pressing issue.
Assignee of the present development, Orbis Corporation has been developing and refining plastic corrugated containers and the processes for forming them. Examples of recent Orbis Corporation developments are described in U.S. patent application Ser. No. 14/265,977, filed Apr. 30, 2014, titled “Plastic Corrugated Container with Sealed Edges”, U.S. patent application Ser. No. 14/265,935, filed Apr. 30, 2014, titled “Plastic Corrugated Container with Manufacturer's Joint Adding Zero Extra Thickness”, U.S. patent application Ser. No. 13/273,019, filed Oct. 13, 2011, titled “Plastic Corrugated Container with Improved Fold Lines and Method and Apparatus for Making Same,” U.S. Patent Application No. 61/920,570, filed Dec. 24, 2013, titled “Plastic Corrugated Manufacturing Process”, and U.S. Patent Application 62/062,481, filed Oct. 10, 2014, titled “Plastic Corrugation”, all of which are incorporated herein by reference.
Aspects of the present invention are applicable for a variety of container and box types. The most common box style is a regular slotted container (RSC) having four side panels with four top flaps (for forming a top) and four bottom flaps (for forming a bottom). For a rectangular shaped box, the two longer flaps are referred to as the major flaps and the two shorter flaps as the minor flaps. Another common box style is a half slotted container (HSC). The HSC is similar to the RSC except that it only includes the bottom set of flaps and has an open top. In the HSC, the top edge of the blank used to form the box becomes the upper edge of the box side panels. Other types of boxes (e.g., autolock, auto erect or crash lock boxes—ALB) can also be formed using various aspects of the invention as well.
The present invention is provided as an improved plastic corrugated container and process for forming the container.